Electric convector heater

ABSTRACT

An electric convector space heater comprises a convector wire helix which is wound helically around a tubular support with the loops of the helix extending radially from the support and a heat source in the form of an electric resistance wire which is also wound around the tubular support and has means for connecting its ends to a source of electric current. In one form of the invention the convector wire helix is electrically insulated from the support and itself forms the electric resistance wire and in another form of the invention the electric resistance wire is in the form of an element in which it is surrounded with an insulating coating and a metal sheath. The element is wound helically around the support between the turns of the helical winding of the convector wire and the sheath is entirely encased in solder or brazing metal by which the element and the convector wire helix are fixed to the support.

United States Patent 1191 Roffelsen 1 ELECTRIC CONVECTOR HEATER [76] Inventor: Franciscus Roffelsen, Mauritslaan 7,

Helmond, Netherlands [22] Filed: Jan. 16, 1970 [21] Appl. No.: 3,390

[30] Foreign Application Priority Data Jan. 20, 1969 Germany P 19 02 575.3

52 us. c1. 219/365, 165/184, 219/342,

51 Int. Cl. H05b 3/02, F24h 3/00, H016 3/00 [58] Field of Search 219/342, 341, 365,

1 June 19, 1973 206,740 2/1968 U.S.S.R 219/553 Primary ExaminerA. Bartis Attorney-Arthur O. Klein [57] ABSTRACT An electric convector space heater comprises a convector wire helix which is wound helically around a tubular support with the loops of the helix extending radially from the support and a heat source in the form of an electric resistance wire which is also wound around the tubular support and has means for connecting its ends to a source of electric current. In one form of the invention the convector wire helix is electricallyin sulated from the support and itself forms the electric resistance wire and in another form of the invention the electric resistance wire is in the form of an element in which it is surrounded with an insulating coating and a metal sheath. The element is wound helically around the support between the turns of the helical winding of the convector wire and the sheath is entirely encased in solder or brazing metal by which the element and the convector wire helix are fixed to the support.

6 Claims, 11 Drawing Figures Patented June 19, 19 73 3,740,527

Inventor: v

fianciscus Raf/else! Patented June 19, 1973 3,740,527

3 Shah-Shoot 3 (PP/0R 42 r) Inventor:

Finalise Rz ialsen by: M

AHOrncu Patented June 19, 1973 3 Shuts-Shoot 5 felsen n a Tm ELECTRIC CONVECTOR HEATER This invention relates to electric convector space heaters particularly for heating living rooms and the like.

It makes use of a known form of heat exchanger comprising a convector wire helix which is wound helically around a tubular support with the loops of the helix extending radially from the support, the loops having a greater radial dimension than their axial dimension.

Previously however these heat exchangers have been used for transferring heat from fluid, such as hot combustion gases flowing over the helix through the wall of the tubular support to another fluid flowing through the support or alternatively from a fluid flowing through the support to the atmosphere surrounding the helix.

The object of the present invention is to provide a heat exchanger of the form just described, differing however in that there is no fluid flowing through the tubular support and thus there are no pipes connected to the support, the heat being produced in the heat exchanger itself from a supply of electrical energy. Furthermore, in order to obtain the lowest possible production costs, and the greatest possible adaptability to suit different requirements, the heat exchanger is preferably constructed in such a way that it can be produced continuously and then cut off into sections of the desired lengths, to form the final product.

According to this invention, an electric convection space heater comprises a heat exchanger of the form described together with a heat source in the form of an electric resistance wire wound helically around the tubular support and means for connecting the ends of the electric resistance wire to a source of electric current.

Preferably the electric resistance wire is surrounded by a coating of an electrically insulating substance. The insulated resistance wire can be wound around the carrier quite close to the looped convector wire helix so that heat can flow easily from the resistance wire to the convector wire. Alternatively however if desired the convector wire helix can itself form the electrically insulated resistance wire.

In the first of these two cases the electric resistance wire, which is electrically insulated by a coating, is enclosed in a closely fitting metal sheath, for example a copper sheath or a woven silver wire sheath, the whole element thus formed being wound on the support. The metal sheath is brazed or soldered to the convector wire helix in such a way that the brazing metal or the solder entirely surrounds the sheath of the resistance wire, so that the heat is easily conducted from the electric resistance wire to the convector wire helix. The insulation of the heating wire can for example consist of a thin fibrous layer or a thin layer of a plastics material. This electrically insulating layer should be thin firstly to facilitate the flow of heat, and secondly to give good flexibility when the electric resistance wire is being wound around its support.

An electric heating element of this kind can very well be used because its temperature need rise only to about 60 100 C, due to the very rapid removal of heat by the convector wire helix, which has a large surface and rapidly surrenders the heat to the surrounding atmosphere. At these comparatively low temperatures practically all the usual fibrous insulators and lacquer coatings are stable and durable. Moreover insulating sheaths are known for electric wires which are capable of withstanding much higher temperatures even though the coatings themselves are very thin, for example electrically insulating coatings made of glass fibres or of certain plastics substances, which can be applied to the wire in liquid form either by dipping or by spraying. The electrically insulating coating of the heating wire should have good heat conducting properties and should contain as few air bubbles as possible.

The electrically insulated resistance wire closely surrounded by its metal sheath may be coiled around the support between the turns of the helical winding of the helix, or if desired within the loops of the convector wire helix. The metal sheath of the resistance heating wire is brazed or soldered to the neighbouring parts of the looped convector wire helix in such a way that the heat generated in the resistance wire is conveyed with the least possible resistance to flow from the heating wire to the convector wire. The brazing metal or solder should entirely surround the sheath of the heating wire, so as to give the greatest possible heat transfer crosssection for the outward flow of heat.

As an alternative arrangement the electrically insulated heating wire in its metal sheath can if desired be mounted by winding it around the outside of the convector wire helix, the metal sheath of the heating wire being in this case brazed or soldered to the outer peripheral surface of each loop of the convector wire helix. This arrangement has the advantage that the heating wire helps to locate and support each loop of the convector wire helix, which is is usually made of a very thin and soft wire for example copper. The heating wire acts as a stiffener for the loopsof the convector wire helix, preventing deformation of the latter during assembly and transportation, and during maintenance operations when the heater is in use.

In a particularly simple form of the heater in accordance with the invention, the convector wire helix itself forms the resistance wire. With heaters of the usual length of about 3 feet the convector wire helix can be made of a fairly thin wire, for example of a diameter of 0.5 mm. The customary mains electrical supply voltage then allows a convector wire helix of copper wire to be used. On the other hand, in the case of a shorter heater of comparatively low heat output, the wire is preferably made of iron, giving a correspondingly low cost of manufacture for the heater. Where the resistance wire is contained in a copper sheath, the insulation must be as dense as possible, to prevent inclusions of air. In contrast to this the insulation of a resistance wire formed by the looped convector wire helix can be porous and can even have interruptions, because the insulation serves merely to prevent electrical contact between neighbouring wire loops, and as a protection against touching from outside.

The loops of the convector wire helix may be inserted fairly closely spaced apart into the surface of a support made of an electrically insulating material, and if the heat exchanger is surrounded by a protective housing preventing the wires from being touched from outside, then there is no necessity to provide any insulating coating on the heating wire, which may then be bare and uninsulated.

The heater may then easily be manufactured by winding the convector wire helix under tension on a support made of an electrically insulating material, the wire helix being then attached to the support by an electrically insulating adhesive. Alternatively, the convector wire helix can be wound under tension on a support made of a thermo-plastic plastics material the surface layer of which is then melted, for example by high frequency heating, to anchor the wire helix by introducing the radially inner parts of the loops into the support.

Several examples of heaters in accordance with the invention will now be described with reference to the accompanying drawings in which:

FIG. 1 is a longitudinal section through part of a first example;

FIG. 2 is a detailed section to a larger scale of the example shown in FIG. 1;

FIG. 3 is a section similar to FIG. 2, but of a second example;

FIG. 4 is a cross section through a third example;

FIG. 5 is a longitudinal section through the complete heater, part of which is shown in FIG. 1;

FIG. 6 is an end elevation of the heater shown in FIG.

FIG. 7 is a detailed section showing a variation of the third example illustrated in FIG. 4; 7

FIG. 8 is a detailed section showing a portion of the third example illustrated in FIG. 4;

FIG. 9 is a detailed section showing an example of the manner in which the convector wire helix can be fastened to the tubular support;

FIG. 10 is a detailed section showing another example of the manner in which the convector wire helix can be fastened to the tubular support; and

FIG. 11 is a detailed section showing a known prior art manner in which the convector wire helix is made of metal and is soldered to the tubular support.

In the example shown in FIG. 1, a wire helix is wound helically around a tubular support 2, the loops of the helix being spaced fairly closely together but nevertheless leaving gaps between neighbouring loops. The loops of the wire helix extend radially from the support 2 and each loop has a greater radial dimension than its axial dimension. Wound on the tubular support 2 be- 4 tween the turns of the helical winding there is a heating element 3 containing a resistance wire the two ends of which are arranged to be connected to an electric cur-. rent source. Around the outside of the turns of the convector wire helix 1 there a stiffening wire 10 is wound and this is brazed or soldered to each loop la of the helix 1. The stiffening wire 10 retains the loops of the convector wire helix so that they remain equally spaced apart around the helix as shown in FIG. 1 and in the same manner as wire 3 spaces the turn of helix 1a in FIG. 4.

As will be seen from FIG. 2 each heating element 3 consists of a resistance wire 3a covered by an insulating coating 3b and, over this, a metal sheath 3c. The metal sheath 3c is soldered or brazed to the loops la of the convector wire helix in such a way that the solder or brazing metal 4 entirely encloses the resistance element 3. The solder or brazing metal also fills at least partly the spaces between neighbouring loops la. Consequently the heat produced in the heating wire 3a is transferred almost completely to the looped convector wire helix 1.

The example shown in FIG. 3 differs from the example of FIGS. 1 and 2 only in that insulation 3b and a metal sheath 3c surrounding the heating wire 30' are deformed to give an approximately triangular cross section, this arrangement allowing the loops la of the convector wire helix to be spaced closer together on the support 2.

In the example of the heater shown in FIG. 4, radially inner parts of the loops la are spaced apart around the path of the helical wrapping leaving a gap 5 between each pair of neighbouring loops. The looped convector wire helix is wound on a tubular support 2a made of an electrically insulating material. The convector wire helix is attached to the support 2a by means of an electrically insulating adhesive as shown in FIG. 10. In this case a heating element 3" is wound around the outside of the helix 1 and is soldered or brazed to each loop la of the helix, again in such a way that the solder or brazing metal entirely surrounds the heating element as shown in FIG. 8.

Another example of the invention in which the looped convector wire helix itself forms the electrical heating wire element is illustrated in FIGS. 7, 9 and 10. Its construction can easily be described by reference to FIGS. 4, 7, 9, and 10. In this case the looped convector wire helix 1a forms the heating wire element and the wire 10 wound around the outside of the helix is of electrically insulating material. The wire 10' is fixed by means of an adhesive as illustrated in FIG. 7 to the outer surfaces of the convector wire loops, the function of the wire 10' being merely to stiffen the wire helix and retain the individual loops la correctly spaced apart in the same manner wire 3" retains the loops of helix la in FIG. 4, where a stiffening wire 10 is illustrated. Instead of fixing the loops of the helix In to the support by an electrically insulating adhesive as shown in FIG. 10 the support itself may be made of thermoplastic plastics material and the inner parts of the loops are then introduced into the surface of the support by heating it as shown in FIG. 9.

There are thus illustrated and described the following different embodiments:

1. An insulated resistance wire is covered with a metal sheath and is mounted within the individual tubes of the convector wire helix around the tubu lar support (FIGS. 1, 2, and 3).

2. An insulated resistance wire covered with a metal sheath is mounted on top of the outer peripheries of the individual loops of the convector wire helix and is soldered and brazed along the contacting surfaces to the convector wire helix (FIGS. 4 and 8).

3. The convector'wire helix itself consists of an insulated resistance and heating wire and is supported on the tubular support (not illustrated).

4. a. The convector wire helix itself consists of blank resistance wire;

b. the individual loops of the convector wire helix are uniformly spaced on a tubular support by being wound thereon and a tensioned wire is wound around them to stiffen and strengthen the assembly;

0. the tubular support consists of insulating material and the individual loops are glued onto or embedded into the tubular support (FIGS. 7, 9, and 10). The convector wire helix is stiffened by insulated wire or a wire consisting of an insulating material (this is necessary because in the em bodiment of FIG. 7 the convector wire helix must be made of very thin wire in order to produce the require high electrical resistance; consequently the danger exists that the mechanically weak loops are bent and thereby produce short circuits).

Referring to FIGS. 5 and 6, a looped convector wire helix is wound around a supporting tube of the type shown in FIGS. 1-3 so as to provide proper antecedent basis for claim 8. Accordingly, the hatching of tube 2 in FIG. 5 has been left unchanged. The supporting tube is retained between two similar end pieces 7 which are tied together by a metal tie rod 6. The end pieces 7 are made of an electrically insulating material. In each end piece 7 two electric contact prongs 8, 9 are mounted and these together constitute an electric contact plug. One prong is connected to one end of a heating wire 3a, the other prong being electrically connected to the tie rod 6. In this heater current may be supplied to the heating wire 3a, from an electric current source through the two prongs 8, or alternatively if desired through the prongs 8 and 9 at one end of the heater, the prongs 8 and 9 at the other end of the heater being directly connected together electrically. If desired a number of heaters of this kind can easily be connected together in series or in parallel by means of connecting sleeves and short circuiting connectors. The end pieces 7 can serve for securing the heater in a housmg.

Although the invention is illustrated and described with reference to a plurality of embodiments thereof, it is to be expressly understood that it is in no way limited to the disclosure of such a plurality of preferred embodiments, but is capable of numerous modifications within the scope of the appended claims.

I claim:

1. An electric convector space heater comprising a tubular support, a convector wire helix wound helically around said support with loops of said helix extending radially therefrom, said loops having a greater radial dimension than the axial dimension thereof, means fixing said helix to said support and electrical heat source means including insulated electric resistance wire means surrounded by a closely fitting metal sheath and wound helically around said support so as to form a double helix with said convector wire helix, and means for connecting the ends of said electric resistance wire means to a source of electric current.

2. A heater as claimed in claim 1, wherein said insulated electric resistance wire means comprises an electric resistance wire, a coating of electric insulation surrounding said wire and said closely fitting metal sheath surrounds said coating, said electric resistance wire means being wound helically around the outside of said convector wire helix and a fused metallic bond fixing said metal sheath to the loops of said helix, said fused metallic bond entirely surrounding said metal sheath at each point where said metal sheath is fixed to one of said loops.

3. A heater as claimed in claim 1, further comprising filament means wrapped helically around loops forming said convector wire helix, said filament means being fixed to the peripheries of said loops.

4. The electric convector space heater as set forth in claim 1, wherein said insulated electric resistance wire means includes an electric resistance wire, a coating of electric insulation surrounds said wire, and said closely fitting metal sheath surrounding said coating, said electric resistance wire means being wound on said support between the turns of said helically wound convector wire helix and fused metallic bond said metal sheath to adjacent loops of said helix, said fused metallic bond entirely surrounding said metal sheath.

5. An electric convector space heater comprising a tubular support, a convector wire helix which is wound helically around said support with loops of said helix extending radially therefrom, said loops having a greater radial dimension than the axial dimension thereof, means fixing said helix to said support and electrical heat source means including electric resistance wire means wound helically around said support and including an electric resistance wire, a coating of electric insulation surrounding said wire, and a closely fitting metal sheath surrounding said coating, said electric resistance wire means being wound on said support between the turns of said helically wound convector wire helix and a fused metallic bond adhering said metal sheath to adjacent loops of said helix, the metal of said bond entirely surrounding said metal sheath, and means for connecting the ends of said electric resistance wire means to a source of electric current.

6. A heater as claimed in claim 5, further comprising a pair of end pieces, means mounting said support between said end pieces, a metal tie rod extending through said support between said end pieces and clamping said support therebetween, a pair of electric contact prongs fixed to each of said end pieces, means electrically connecting one of said prongs on each end piece to the adjacent end of said resistance wire means and means electrically connecting the other of said prongs on each end piece to said tie rod. 

1. An electric convector space heater comprising a tubular support, a convector wire helix wound helically around said support with loops of said helix extending radially therefrom, said loops having a greater radial dimension than the axial dimension thereof, means fixing said helix to said support and electrical heat source means including insulated electric resistance wire means surrounded by a closely fitting metal sheath and wound helically around said support so as to form a double helix with said convector wire helix, and means for connecting the ends of said electric resistance wire means to a source of electric current.
 2. A heater as claimed in claim 1, wherein said insulated electric resistance wire means comprises an electric resistance wire, a coating of electric insulation surrounding said wire and said closely fitting metal sheath surrounds said coating, said electric resistance wire means being wound helically around the outside of said convector wire helix and a fused metallic bond fixing said metal sheath to the loops of said helix, said fused metallic bond entirely surrounding said metal sheath at each point where said metal sheath is fixed to one of said loops.
 3. A heater as claimed in claim 1, further comprising filament means wrapped helically around loops forming said convector wire helix, said filament means being fixed to the peripheries of said loops.
 4. The electric convector space heater as set forth in claim 1, wherein said insulated electric resistance wire means includes an electric resistance wire, a coating of electric insulation surrounds said wire, and said closely fitting metal sheath surrounding said coating, said electric resistance wire means being wound on said support between the turns of said helically wound convector wire helix and fused metallic bond said metal sheath to adjacent loops of said helix, said fused metallic bond entirely surrounding said metal sheath.
 5. An electric convector space heater comprising a tubular support, a convector wire helix which is wound helically around said support with loops of said helix extending radially therefrom, said loops having a greater radial dimension than the axial dimension thereof, means fixing said helix to said support and electrical heat source means including electric resistance wire means wound helically around said support and including an electric resistance wire, a coating of electric insulation surrounding said wire, and a closely fitting metal sheath surrounding said coating, said electric resistance wire means being wound on said support between the turns of said helically wound convector wire helix and a fused metallic bond adhering said metal sheath to adjacent loops of said helix, the metal of said bond entirely surrounding said metal sheath, and means for connecting the ends of said electric resistance wire means to a source of electric current.
 6. A heater as claimed in claim 5, further Comprising a pair of end pieces, means mounting said support between said end pieces, a metal tie rod extending through said support between said end pieces and clamping said support therebetween, a pair of electric contact prongs fixed to each of said end pieces, means electrically connecting one of said prongs on each end piece to the adjacent end of said resistance wire means and means electrically connecting the other of said prongs on each end piece to said tie rod. 